This invention relates to a sensor panel and to a detection apparatus incorporating the same. The sensor panel uses magnetic fields to detect the presence of particular materials.
Detection apparatuses are commonly used to detect the presence of metal objects on or about persons entering a secure area, such as an airport.
Existing detection apparatus consist of an archway through which pedestrians walk. A single coil is connected to an oscillator, and produces an alternating magnetic field in the archway. The coil is driven by the oscillator at a tapping that is a fraction of the total turns. The signal at the total turns is utilized to detect the change in the magnetic field caused by metallic objects passing through the magnetic field.
Detection apparatus of this type are useful in providing an indication that a metal object exists, but do not give any information about the location or shape of the object. Consequently, at present security guards with hand-held detectors are used to locate the object once the existence thereof has been detected.
In accordance with the present invention there is provided a magnetic detection apparatus for sensing an object in a sensing region, the apparatus including:
a magnetic field generating means for producing a magnetic field within said sensing region in response to a source signal;
a plurality of magnetic receiving elements arranged in a matrix, each magnetic receiving element being responsive to changes in the magnetic field within the sensing region to provide an output signal;
cancellation means for generating a feedback signal adapted to minimise spurious magnetic effects of the magnetic field generating means on the output signals of the magnetic receiving elements; and,
signal processing means for processing said output signals of the magnetic receiving elements and producing an image corresponding to variations produced in said output signals by the object in the sensing region whereby, in use, an indication of the location and approximate shape of the object in the sensing region can be obtained.
In one arrangement, the cancellation means comprises a feedback coil arranged to be excited by the source signal, the feedback coil inducing a feedback signal in each magnetic receiving element to negate the effects of the magnetic field generating means.
In an alternative arrangement, the cancellation means comprises a plurality of feedback coils, one for each magnetic receiving element, wherein each feedback coil is provided in close physical proximity to a corresponding magnetic receiving element, each feedback coil inducing a feedback signal in its corresponding receiving element to negate the effects of the magnetic field generating means.
In a further alternative arrangement, the cancellation means comprises a plurality of feedback coils, each coil contributing a portion of a feedback signal, first switching means arranged to selectively isolate each feedback coil so as to remove its contribution to the feedback signal, and second switching means arranged to combine said feedback signal with each output signal in turn.
Preferably, the cancellation means further comprises memory means for storing information concerning which feedback coils are to be isolated for each receiving element.
Preferably, each of said magnetic receiving elements are provided in a substantially planar configuration so as to form a sensor panel.
Preferably, each magnetic receiving element comprises a receive coil.
Preferably, each receive coil is wound on a bobbin, the bobbins being provided on the sensor panel.
Preferably, the position of the bobbins are adjustable in a direction transverse to the plane of the sensor panel whereby the output signal from each receive coil in the absence of any object in the sensing region can be minimised.
Preferably, each receive coil is provided on a printed circuit board as a spiral track thereon.
Preferably, wherein the printed circuit board is a multi-layer printed circuit board.
Preferably, the magnetic field generating means comprises a transmit coil.
Preferably, the transmit coil is provided around the periphery of the matrix of magnetic receiver elements.
In one arrangement, the magnetic field generating means comprises a first and a second transmit coil connected to an oscillator, said transmit coils being provided in a substantially parallel, spaced apart manner on opposing sides of a predetermined volume.
Preferably, the magnetic field generating means, the magnetic receiving elements and the cancellation means form a sensor panel.
Preferably, the signal processing means is arranged to further process the output signals from said receiving elements by one or more of the following methods: interpolation, Fourier analysis, edge detection, or boundary collapsing.
Preferably, the magnetic detection apparatus further comprises a camera arranged to take pictures of the volume, said image being superimposed on the pictures of said volume.
Preferably, said signal processing means is responsive to the phase and amplitude of the output signals from each receiving element to determine therefrom the type of material being detected.